1. Technical Field
The present invention relates to the field of digital control over analog signals. More specifically, the present invention relates to the field of analog amplifiers, such as those used for microphone preamplifiers, that have digitally-controlled gain.
2. History of Related Art
Past generations of microphone preamplifiers have used switched resistances to set the circuit gain by digital control. A computer or other digitally-based controller is normally used to access relays for switching the circuit's gain determining resistances. With such a method, small increments of gain control for smooth circuit gain adjustment are impractical to achieve. Therefore, relatively large steps in gain adjustment are provided for commonly available amplifiers. However, microphone preamplifiers usually require much more subtle and smooth gain control. It would therefore be useful and desirable to provide a digitally-controlled analog gain stage that allows relatively small gain increment adjustments for such uses.
In recent years, digitally-controlled analog electronic gain elements including digital potentiometers, digitally controlled amplifiers or attenuators, and Multiplying Digital-to-Analog Converters (hereinafter "MDACs") have become available. Such elements are widely used in a variety of industrial and consumer electronics equipment, but are too noisy in terms of both digital and thermal noise for use in low-noise microphone preamplifier applications. It therefore would be useful and beneficial to provide a digitally-controlled low-noise variable-gain amplifier that is suitable for use as a microphone preamplifier or in other low noise analog signal applications.